The Google Wifi should be set to PPPoE and you would need to enter your connection userid and password which you will need to get from Vodafone. When you do this it may help if you choose a router on the BT SIN 498 list and if asked, say that is what you intend to use.

A Windows 10 PC can be configured to connect the DM200 using PPPoE as a method of testing.

I setup my Netgear DM200 and it connected to the internet in router mode and updated the firmware. I then switched it to bridge mode (modem only) and it was confirmed that it was still connected to the internet,

I then attempted to connect my google wifi but the google wifi could not connect to the internet and made me go through a rebooting process multiple times.

Connect the normally covered up Wan port of the Vodafone router to the DM200. If the Vodafone router does not get a connection to the Internet (green light on top) the DM200 is not configured correctly.

If that is on the DM200 I don't know, but does not sound as if you need it. The Vodafone router just needs to be switched on and will work provided it was previously working when directly connected to phone line.

I had the DM200 setup with TalkTalk as that is what I used at my last address, I didn’t change a thing on the setup, just plugged it in and put the Ethernet into my Google Wifi. It asked for the PPPoE details on setup for Google WiFi and has worked fine ever since.